1. Field of the Invention
The present invention is related to a cooling system and more particularly to a cooling system mounted in a hybrid vehicle.
2. Description of the Related Art
In recent years, hybrid vehicles have been propagating in which an internal combustion engine, a motor for driving the vehicle and a generator for generating electricity are mounted. As a configuration of a conventional hybrid vehicle, there is known a configuration in which a motor and a generator are disposed coaxially in a transverse direction of the vehicle (refer to Patent Document 1).
Although the motor and the generator are heated to high temperatures while the hybrid vehicle is driven, since the heat resistance temperatures of the motor and the generator are limited, a cooling system is provided for cooling them by recirculating oil or water in general through a coolant piping by a pump. Thus, the motor and the generator are cooled by the common cooling system.
Here, an example of a conventional cooling system for a motor and a generator in a hybrid vehicle will be described. FIG. 5 is an exemplary diagram showing a state in which an oil pump in the conventional cooling system is operating. In addition, FIG. 6 is an exemplary diagram showing a state in which the oil pump in the conventional cooling system is stopped.
As shown in FIGS. 5 and 6, a conventional cooling system includes an oil cooler 102 for cooling oil which cools the motor 100 and an oil pump 101 for pumping oil. The motor 100 is mainly made up of a rotor 100a and a stator 100b which are set concentrically within a housing 100c. Coils are wound around the stator 100b of the motor 100 (the illustration of which is omitted). An oil reservoir 100d is formed in a bottom portion in an interior of the housing 100c of the motor 100 for preventing the oil pump 101 from drawing air thereinto.
A first oil piping 103 is placed between a lower portion of the motor 100 and the oil pump 101. Oil reserved in the oil reservoir 100d in the motor 100 is supplied to the oil pump 101 through the first oil piping 103. A second oil piping 104 is placed between the oil pump 101 and the oil cooler 102. Oil pressurized by the oil pump 101 is supplied to the oil cooler 102 through the second oil piping 104.
A third oil piping 105 is placed between the oil cooler 102 and an upper portion of the housing 100c of the motor 100. Oil cooled in the oil cooler 102 is supplied to the motor 100 through the third oil piping 105. The oil discharged from the third oil piping 105 is poured on to an upper portion of the stator 100b of the motor 100. Accordingly, the rotor 100a and the stator 100b of the motor 100 are cooled.
When the oil pump 101 is in operation, oil is recirculated in a direction indicated by arrows in FIG. 5 through the first oil piping 103 to the third oil piping 105. Hence, when the oil pump 101 is in operation, oil is filled in the first oil piping 103 to the third oil piping 105, and therefore, a level 100e of oil in the oil reservoir 100d in the motor 100 is positioned low.
As shown in FIG. 6, however, when the oil pump 101 is stopped, the oil filled in the first oil piping 103 to the third oil piping 105 is returned to be reserved in the oil reservoir 100d in the motor 100. Therefore, the position of the oil level 100e rises, whereby the rotor 100a of the motor 100 is partially submerged in oil.
In FIGS. 5 and 6, the description is made by showing only the motor 100 as an example of a constituent component. Conventionally, since the motor 100 is disposed coaxially with the generator in the transverse direction of the vehicle, the levels of oil in the motor 100 and the generator are positioned in the same level. When the motor 100 and the generator have the same size, a rotor of the generator is also partially submerged in oil.
In the hybrid vehicle described above, when the temperatures of the motor 100 and the generator are low, the oil pump 101 is operated intermittently, and therefore, there is a situation in which the rotors 100a of the motor 100 and the generator rotate when the oil pump 101 is stopped.
In a series hybrid vehicle in which a motor 100 is driven by using electric power generated in a generator, both the motor 100 and the generator operate in a series driving in which the motor 100 is driven by using electric power generated in the generator. In addition, in an EV driving in which the motor 100 is driven by using electric power of a high-voltage battery, only the motor 100 operates. Because of this, the frequency with which the motor 100 operates becomes high.
However, as has been described above, when the oil pump 101 is stopped, the rotor 100a of the motor 100 is partially submerged in oil reserved in the oil reservoir 100d in the motor 100, and therefore, the rotor 100a of the motor 100 stirs oil in the oil reservoir 100d. Because of this, a stirring resistance is produced in the rotor 100a of the motor 100, leading to a problem that the rotation of the rotor 100a of the motor 100 is disturbed.
[Patent Document 1] JP-A-2010-163053